Light-modulator display means



June 28, 1960 A. H. ROSENTHAL LIGHT-MODULATOR DISPLAY MEANS 2Sheets-Sheet 1 Filed March 9, 1954 rt ll :I J INVENTOR ADOLP/r' HIPOSE/VTHAL MODULATING ATTO R N EYS MEANS INPUT FROM RADAR June 28, 1960A. H; ROSENTHAL LIGHT-MODULATOR DISPLAY MEANS 2 Sheets-Sheet 2 FiledMarch 9, 1954 m w W 5 W mw m s Ts Z W H w E 9 4 0 n A M M WW TMMW W R wA m \I 7 R R m 9 Z A K 0 Ma W WWW 815 U W 6 H. o m M 5 N M q 2 w 0 9 a 66 I a, 5 e e RE 50 kw 5 0 w R m m a 1 6. m F F FIG. 8.

FIG. 9.

194041? IPECE/I/EP,

FIG. IO.

INVENTOR w m 5 E 5 N 0 R F m d T W A m m In said drawings, which show,for illustrative: purposes United at nt aaiiasrs r a LIGHT-MODULATORDISPLAY MEANS Adolph H. Rosenthal, Forest Hills, N.Y., as'signor m'Fairchild, Camera and Instrument Corporation, Syosset, N.Y., acorporation of Delaware a a Filed Mar. 9, 1954, Ser. No. 415,055 I 16Claims. c1. 343-17 This invention relates to color-display means andincor- Patented June 28, 1960 and therefore will be treated here only asfar as necessary'tfor the color aspects. In the schematic of Fig. 1,there is shown a color modulator on an optical axis 14. In thismodulator, white or substantially panchromatic light. from a sourcepasses through a condenser-lens system 11 andshutter means 9 (in amanner and for a porates improvements over the disclosure in my PatentNo. 2,513,520, issued July 4, 1950. The presentapplication is acontinuation-in-part of my copending application Serial No. 217,104,filed March 23, 1951, now Patent No. 2,807,799.

It is an object of the invention to provide improved means whereby colorcan be controlled by means of a light-modulating device of theultrasonic-cell type.

Another object-is to provide improved display means incorporating colormodulation. 1 It is also an object to provide improved display meansincorporating intensity modulation and color modulation. It is aspecific object to provide color-modulating means of theultrasonic-celltype for radar, oscillographic,

purpose to be later described) to a diaphragm 13 having a' slit 12formed therein. The light passing this slit 12 is collimated, or madeparallel, by a lens 17 and traverses as parallel beams the ultrasoniccell 15; thereafter, the light is concentrated by lens 18 upon thediaphragm '19. In other words, the optical system consisting of the twolenses 17 and 18, and of the ultrasonic cell 15, forms at 20 an image ofthe slit 12 in diaphragm 13 upon the plane of diaphragm 19. LWhen thecrystal .16 is excited, ultrasonic waves will be produced in the liquidof the cell 15, and these waves will ditfract the parallel beams fromtheir original direction; a number of diffraction spectra will then beformed upon the plane of diaphragm 19,"to each side of the center 20 ofthis diaphragm, or to each side of theoriginal slit image. Each of thesediffraction spectra constitutes a separation of the light from source 10into its component colors.

In past applications of the ultrasonic light modulator, the slit 12 ofdiaphragm 13 has usually been ,made so wide that the color spectrabelonging ,to individual sur- 7 face parts of this slit openingoverlapped in the plane of and other time-based or otherwise-baseddisplay of detected-phenomena. t 1

Another specific object is to provide means for storing in anelectro-optical display deyice, for short intervals, a plurality ofobserved parameters as a function ofthe same time base andforeffectively projecting the stored data in a single presentation coveringthe full or a selected part of said time base, one of the parametersappearing as an intensity or brightnessmodulation and the other as acolor modulation over said timebase. i

It is a further specific object, to provide means for elfectivelyinstantaneously sampling a delay line which.

has been impressed with amplitude-modulated and frequency-modulated dataand for optically displaying, from such sampling, an intensity orbrightness modulation and a color modulation overa common time scalerepresenting transit time along said delay line.

It is a general object to achieve the above objects with apparatus ofrelative simplicity, involving virtually no further parts than thoseemployed in analogous blackand-white displays. v

Other objects and various further features of novelty and invention willbe'pointed out or will occur to those skilled in the art from a readingof the. following specification in conjunction with the accompanyingdrawings.

only, preferred forms ofthe invention:

Fig. 1 is a simplified 'isometricdiagram, schematically showing opticalelements of a display means incorporating features of the invention;

Fig. 2 is a simplified diagram to explain ing of a part of the apparatusof Fig. 1; 2 V

Fig. 3 is a circuitdiagram ofcontrol meanslfor the apparatus of Fig. 1,certain of the optical parts of Fig. 1 being shown enlarged andin asection-through the plane 33 ofFig. 1; Figs. 4, 4A and Sara simplified'diagrams of alternative display means of the invention; and

Figs. 6 to 10 are block diagrams of variousradar applications of thedisplaymeans of the invention.

- The scientific basis of ultrasonic color modulation is thefunctionthis theory has been .discussed at length in the literature,

diaphragm 19in such away, as to produce substantially white lightthereon. In other words, the inherent spectralresolution of theultrasonic diffraction grating-was not utilized, because the mainproblem was to obtain a maximum of black-and-white light modulation. Bymaking the slit opening 12in the diaphragm lii sufirciently'narrow, truecolor-diffraction spectra can beproduced at the plane of diaphragm 1'9.i

The position of such color-diffractionspectra'is shown in Fig. 2, where14 is the optical axisand 20 indicates the central position on diaphragm19, as in Fig. 1. On the plane of diaphragm 19 are shown the firstandsecond-orde'r spectra on each side of the central position 20; theapproximate relative positions of wave-lengths, from the violet end (at4000 Angstrom units) to the red end (at 7000 A.) are indicated.

Fig. 3 will serve to illustrate the color-diffraction phenomenon withgreater detail. In Fig. 3, the position of one of the first-orderspectra is schematically indicated of. ultrasonic-lightditfractionsin'front of the diaphragm 19, and the positions of thecolors blue, green, and red for a particular diifraction condition areindicated by the letters b, g, r, respectively. Since the placement ofparticular colors is proportional to the wavelengths of these colors,red will be further displaced than green and blue, for a givendilfraction condition; three such ditfraction conditionsare depicted atI, II, and III. By arranging a 'slit opening 21 (in diaphragm 19) at adistance d from the central position 20, and, 2 depending upon theplacement of this slit opening withv respect to thecenter 20 for givendiffraction conditions, any particular color can be made to pass theopening 21, the other colors being stopped by the diaphragm 19. Thedevice may thus act as a spectroscopic monochromator of selectableWavelength.

- Referring again to Fig. 3, it. will be seen that one may predict theconditions under which a particular color of wavelength A will be.positioned'at a distance d from the center-20. of the diaphragm 19 thus,from the theory AN ti rof lens to the diaphragm 1 9, A is the wavelengthof light, N is the carrier'frequency' of the modulation V where f is thefocal length of the lens '18, or the distance impressed upon the crystal16, and v is the velocity of the ultrasonic waves in the liquid of thecell. Importantly, it will be noted from Expression 1 that thedisplacement of any particular color is proportional both to thewavelength 7\ of this color, and to the ultrasonic carrier frequency N,that is, to the frequency of the electric oscillations impressed uponthe crystal 16. Therefore, for any given position of the slits 21 in thediaphragm 19 (i.e., for any given value of d), the wavelength of thelight which can pass through these slit openings 21 is inverselyproportional to the ultrasonic frequency N (i.e., to the electriccrystal-exciting frequency), in accordance with the following expression(derived from Expression 1 above):

Thus, he len h ha s h c lo of he lig t rans-- mitted through thediaphragm 19, can be completely controlled by the frequency N of theelectric oscillations impressed uponthe crystal 1 6; by varying thisfrequency N, the diffraction spectrum may be caused to shift across. theslit opening 21 on diaphragm 19, so that any desired color can be madeto pass the diaphragm 19.

According to previously described principles of ultra-. sonic lightmodulation, light intensity, that is, the intensity of the light (of agiven color), is substantially proportional to the intensity or power ofthe electric oscillations impressed upon the crystal 16. Thus, theintensity of the olle ht m y be gove ned y n; mpl tude modulation of thesignal impressed on crystal 16, while, t th e me n cc da c h he nyenionrthe color of the controlled light may be governed, by a frequencymodulation.

Briefly stated, the invention contemplates novel; means for utilizingvarious combinations of these independent modulating means to controlthe intensity and color of light in a given display system, Stated inother words, the invention may permit the display of two independentvariables characterizing a given phenomenon, by employ ment of the twoparameters of lighttransmitted by diaphragrn 19, namely, its intensityand its; color. In one specific form to be described, two independentvariablesmay be employedin the amplitude and frequency'modula, tion ofthe crystal ofa single ultrasoniccell; inan alter-. nate form, separatecells, separately frequency-modulated and amplitude-modulated, may beemployed in. a single optical system. Regardless of the modu ati means,the light issuing from the diaphragm 19" can be utilized in any desiredmanner, as by employing" an ob.-. jective lens 22; to form an image ofthe ultrasonic-cell modulations on a screen or on. color-responsivefilm, such as Kodachrome, Ansco color, or the like.

In the arrangement of Fig. 1', the single cell may be subjectedsimultaneously to amplitude modulations and to frequency modulations tocorrespondingly control the relative intensity and color of lightissuing past. diaphragm 19. Such light may be focussedby; lens 22; ontoa viewing screen 25-, and lightly outlined area 26 .on screen 25 will beunderstood to designate the optical. image of the effective transverseextent (i.e. normal to the axis 14) of the ultrasonic cell 15.

The shuttermeans 9; may be of any desired type, but for present purposesit should possess sufiicientlyfast action to expose the screen 25 foronly a small fraction (say one percent, orless, depending upondesiredresolu: tion) of the transit timeiin theultrasonic cell 15; In theformofsFig. 1, shutter means fiscomprisesressentially-anelectro-opticalmechanism 27, utilizing 'electro-optic'al active crystal, such asammonium-dihydrogen phosphate (ADP), laminated between transparentelectrodes, and disposed between light polarizers in quadrature; a slitdiaphragm 13 and collimatinglenses- 17--18 may-rassureshutter action onparallel rays as well as anefiicient shutter-controlled illumination ofslit 12. A delayedaction synchronizing-pulse amplifier 27' mayadequately operate the shutter mechanism 27, and the delay in amplifier27 should be such as to apply a shutter impulse at the instant whenultrasonic cell 15 contains a full signal, corresponding to its lengthin terms of the sonictransit time across the cell 15.; in other words,the synchroniz ing pulse to shutter 27 should occur at a particularinstant of time (represented by cell length, divided bythe velocity ofsound). after commencement of application of the desired video signal tothe cell crystal 16. In the type of organization justv discussed, theultrasonic cell 15. will be seen to function essentially as a delay-linemeans.-

A simplified circuit. 28 of a type which may be used to impress theamplitude and frequency modulations upon the crystal 16 is shown by wayof example in Fig. 3. Such a circuit 28 may be of the quadraturevariablereactance type, in which the frequency of a tank circuitincluding an oscillator tube is electronically controlled by voltagesimpressed upon a variable-reactance circuit. In the circuit of; Fig. 3,the tube 30 follows the varying amplitude of the amplitude-determiningsignal (A)- impressed at input 29 to control the amplitude ofoscillations in a tank circuit comprising capacitance 31 and inductance32. The normal oscillating frequency may be selectablydetermined bymanual adjustment at 32, as when adjusting a center frequency or color;and signal-controlled variations from this center frequency may begoverned by variable-reactance tube 33. The frequency-determining signal(F) maybe applied at input 34' to the control grid of tube 33; this gridis also fed; from the; output'circuit of' tube 33 through aphaseshifting resistor-reactance network 3536, thereby caus ing tube 33to produce amplified voltages substantially out of'phasewith the voltageacross the tank circuit. Since the output circuit oftube- 33 is in shuntwith thetank circuit Ell-32, the instantaneous total reactance (and,therefore, the instantaneous frequency) of this circuit depends upon theamplification of the tube 33, andcan therefore be controlled by thefrequency-determining signal (P). The instantaneous amplitude andfrequency of oscillations-in tankcircuit 31-32 may be inductively takenat 37 from inductance 31, for application to crystal 16;

Thus, summarizing, control signals, (A) at input 29- rnodulate theamplitude of oscillations in tank-circuit 31 312, and: thereby determinethe relative brightness or intensity of light passing; through theoptical system of Big. 1,;at the, same time,.contro l signals (F) atinput 34 modulate; the frequency of oscillations in tank. circuit31-.32,, and thereby determine the. instantaneous color of light passingthrough the optical system ofFig. 1. At any; single instant; of; time,there; may be, a spatial distribution of such. amplitude. modulations;and. frequency modulations. along the length of cell. 15, and wheninstantaneouslyviewed, as undertheaction. of shutter 27, the intensityand colordistribution acrossthe image area 26 will reflecttherespective-modulations; a scale maybe inscribedacross screen 25; asshown, inorder to facilitate interpretation of the projectedspatial-distribution data, lt s'hould be noted that the. colormodulation and the intensity modulationachicyed by the above-describedmean may be effected, practically instantaneously, i.e., with; a timeconstant of. the. order of fractions. of microseconds;depending uponthe.circ11it. parameters and the crystal carrier frequency N.

From. Exnresisons; 1.. and):v above; for any desired color, given thefocal.:length;f"of; lens. 18-. andpositionof slit:21, the-.required:carrier frequency N can be calculated. I Thefollowing;table-.shows,;.by:'way;of; example. forthree colors- (blue,- green,red)' the required. frequenci'eeN, under-circumstances in which thefocal length" (1 9) along the spectra;

. number. i

For many applications, it is desirable to havea means of shifting allcolor values within a certain range, either to accommodate to the colorperception of the observer, or to obtain a matching with certainstandard COIIIPBIL- "son colors. The disclosed arrangements lendthemselves to the variable selection of color shift, in numerous ways,including the following:

(a) Selectively changing N, as by selectively varying circuit (see Fig.3).

(b) Selectively shifting a collimating lens (18) across the optical axis14 and generally parallel to the soundpropagating axis of'cell-15, asindlcated at 18' n Fig. 1.

(c) Selectively shifting the slits (21) of a diaphragm in the caseofseveral shts, this shift must be done symmetrically with respect to thecenter 20, and in proportion to the spectrum order the average carrierfrequency the capacitor 32 in the tank (d) Inserting a plane-parallelglass plate 69 between a. colliinating lens and a diaphgram, as nearlens 18, between it and diaphragm 19, and plate to produce inclinationsthereof with respect to a plane transverse to the optical axis 14.

. (e) Inserting between the ultrasonic cell and one of the collimatinglensesan achromatic variable angle prism of the type as used in rangefinders.

All the above or any other color-shifting means can be calibrated andread on a dial, as shown in the cases of indicators 18" and69', so thatany. manually or otherwise selected shift may be used to indicate thevanation of the colordetermining factor,.as will l'ater appear.

The above discussion has shown that an ultrasonic signal-recording ordisplay device can be utilized to represent independently atwo-dimensional array of continuous variables, represented by continuousvariation ingintensity and color of thepicture elements. Both variationscan be controlled by two control voltages to be fed lnto the device,these volt-ages being applied in the same line when feeding a singlecell (as the cell 15 of Fig. 1, Fig. 4A, or the cell 90 of Fig. 5, or intwo separate lines when feeding separate cells asyat 50-51.in Fig. 4).Many applications of this principle may be made, and I shall brieflydescribe a. few radarapplications. In each of these cases, the singlenetwork 28 is schematically shown to have a single output, as in thecase of Figs. 1,

selectively rotating this 8 teristics of the network, suchdiscriminating effects as the following may be achieved: land areas maybe shown in yellow, sea areas in blue; built-up areas may be showii inred, and rural areas in green; air-borne targets may be shown in yellowagainst a blue'background. ac-

tual colors in which the targets appear may be controlled and thecorrelation between echo intensities and colors adjusted in variousways, as by choosing different tapping points, or by employing one ofseveral of the above-described electronic or mechanical color-shiftingmeans.

In certain tactical and mapping or charting applications it is importantunmistakably to identify a particular target, as in the case of aerialsurveying in the field of known ground-based beacons, or in applying LFFtechniques. Radar returns from such objects are coded or. otherwiseparticularly characterized, fSO that by em.- ployment of suitablyresponsive decoding means 70 (Fig. 7) in the video output of the radarreceiver, the video output may be admitted to the color-modulating line34 if desired. With the described arrangement, it will be understoodthat gun-laying, tracking, and search radar 4A and 5, but it will beunderstood that separate ampliresult from the varying echo intensifiesfrom the targets;

in many cases, these echo intensitiesshow great variation for differentclasses of targets, as between land and sea "areas, between metallic andnon-metallic targets, and particularly between air-borne targets, suchas airplanes and missiles, and the sky background. In such cases, avastly increased discrimination between targets may be obtained byutilizing the varying echo return intensities for controlling .the colorof the targets in the display.

The desired discrimination ,may be enhanced in the circuit of Fig. 6 byvariously tapping the output of a network. 66, which may be non-linear,carrying video signals from theradar receiver 65. As shown, the outputof network 66 isla potentiometer 67, tapped at different voltage levelsto provide the intensity-determining voltages (A) and the frequency(color)determini ng voltmay readily distinguish between friend and foe,even in close or confused formation or aircraft or ships, or possibleground vehicles, merely by observing the distinctive contrasting colorsin the presentation.

In Fig. 8 I illustrate how my color-modulating means may be employed asan aid in discriminating the relative movement of targets. Echoes fromvariously moving targets will be characterized by correspondinglyvarious Doppler effects; the Dopplerreturn frequency may be directlytransposed for frequency modulation of an ultrasonic cell, or,preferably, a discriminator 73, may feed the line 34 at thefrequency-determining end of the network 28. With such an arrangement,not only is it possible to distinguish between moving and stationarytargets, but particular colors may be correlated with par: ticularmoving-target radial velocities (i.e., with instantaneous velocitycomponents in the direction of the radar beam). Thus, for example,stationary targets may be shown in green, approaching targets shiftingin color toward the red end of the spectrum, and receding targetsshifting toward the blue end of the spectrum, or vice versa, the more,the greater the relative velocity. This velocity may be directlymeasured by noting the par: ticular extent of manual operation necessaryto effect such a color change in the moving-target presentation that themovingatarget color is reduced to thatof a stationary: target standard;such manipulation may 'be made by one of the several mechanical andelectronic methods which have been described, as by shifting theplane-parallel caused by wind-blown leaves, window-reflector camouflage,and the like. By suitably rotating the plane-parallel plate 69, it willbe seen that echoes due to such clutter may be shifted altogether out ofthe visible spectrum range, while the desired targets become definedwith improved color and intensity contrast. 7

In application to height-finding radars, my invention may improve theease of interpretation of the display by automatically color-modulatingthe received echoes in accordance with the altitude of detected targets;thus, targets at 5,000-ft. altitude or less may be displayed in red, at15,000 feet in yellow, at 25,000 feet in green, and at 40,000 feet inblue. To this end, the amplitude modulating signal can be derived froman azimuth scan, and the frequency modulating, or color-determiningsig-; nal, from an elevation scan; thus, a combined plan and heightdisplay will be obtained in which different colors can be correlated todifferent elevations. As an example, with reference to Fig. 9, thecomputed-elevation output fof lens 18 is 15 inches (38.1 cm), and theslit distance d from the center position 20 is 2 millimeters:

Wavelength, Frequency, N Color (Angstrom units, A) Megacycles/ sec.)Blue 4500 18.7 Green 5400 15.5 Red 6200 13.5

The slit width is determined by the desired color purity, and for mostpurposes a color band of a few hundred Angstrom units (A) will givesufiiciently distinctive subjective color impressions. Thus, forinstance, a slit width of 0.1 mm. will give color bands of from 200 to300 A. in the first-order spectrum, depending upon the position in thespectrum. The above table suggests that in order to cover the wholevisible spectrum, a relatively wide frequency-modulation swing may benecessary; actually, the crystal-frequency variation is in proportion tothe variation of the light frequency. Although the liquid medium in theultra-sonic cell exerts suflicient damping upon the crystal to coverthis frequency range, it may be desirable (in order to obtain a minimumvariation of vibration amplitude, i.e., a flat response, over thisrange) to incorporate special band-widening means, either at the controlcircuit 28 or at the crystal. For instance, the frequency response ofthe crystal can be considerably widened by arranging additional matchingand/or damping layers between the crystal surface and the liquid;alternatively, combined crystals, e.g., crystals formed by cementingtogether two or more crystals of slightly different resonance frequency,will result in coupled oscillations equivalent to a wide response. Suchcombined crystals may be replaced by multiple crystals arranged side byside or by a crystal of wedge shape, the thickness of which variesslightly, preferably in the direction of the optical axis 14; or thecrystal can be loaded with varying masses, as, for instance, by coveringits surface with a thin metal layer, varying slightly in thickness alongthe crystal surface. These are. just some means of either electricallyor mechanically flattening the overall frequency response of the systemor adapting it to any particular desired shape depending upon theapplication.

Instead of using one slit opening 21, two such openings can be used atequal distances from the: center position 20, as shown in Fig. l. Thefigures of the above table are for the first-order spectra only, butsince there will be also higher-order diffraction spectra, these canalso be utilized, if desired, by arranging additional slit openings tointercept the higher orderspectra. Thus, the

second-order spectra may contribute light by arranging openings ofdouble width and at double the off-axis distance d, as compared with theoffsets of the first-order openings 21; this will be clear from Fig. 2.It will be understood that the total light output can be considerablyincreased by employment of such multiple openings.

In accordance with a feature of the invention, ultrasoniccolormodula:tion means of the character described may be used for radarrecording and display, as well as in oscillographic and otherapplications employing time or otherwise-based sweeps; when so employed,the simultaneous presentation of two parameters on the same time base isfound materially to aid interpretation. In the arrangement of Fig. l,the video output of a radar receiver 38 may be fed by lines 2934 toopposite ends of the circuit 2.8. for deriving amplitude andfrequencymodulated signals for simultaneous application to the crysta15. Synchronizing-pulse signals, as derived from the radar-transmissionpulses may be fed in line 39 to amplifier 27 for appropriately delayedshutter actuation. The resulting presentation 26 on screen 25 will thenbe in effect a synchronized stroboscopic array of closely similarspace-distribution patterns of lines of various intensities and. colors.For example, assuming the scale onscreen 25 to represent range, with theorigin at the 6 left (in the sense of Fig. l), the first echo signal 40may be a dull red, and thus represent a weak echo at relatively closerange; at the same time another echo signal 41 may be a brighter green,thus representing a stronger echo at greater range. Any singlepresentation, may thus be characterized by a wide variety of colors andintensities.

In the alternative arrangement of Fig. 4, I employ two ultrasonic cells505-1 in the optical system, one of the cells being used as a kind offocal-plane shutter, to elfectively immobilize the Wave trains in theother cell; circuit means 52 may accept input signals for translationinto separate frequency-modulated (F) and amplitude-modulated (A)outputs based on the same or different carrier frequencies N, and inaccordance with a feature of the invention, one of these outputs(frequency-modulated) may be applied to one cell (50) while the otheroutput is applied to the other cell (51). The optical system maygenerally resemble that of Fig. 1, that is, light from a source 53 maybe focussed by condenser 54 on the slit of a first'diaphragm 55. Lightpassing diaphragm 55 may be collimated by lens 56 for passage throughthe first cell 50 and then focussed by lens 57 on the stop betweendiffraction slits of a second diaphragm 58. The ultrasonic Waves of cell50 are imaged upon cell 51 by lens 59 and collimated by lens 60, forpassage through the second cell 51. Thereafter, the light may befocussed on the slit of a third diaphragm 61, and subsequently projectedby a lens 62 onto a viewing screen or recording medium 63. In the formshown, shutter action is achieved in the first cell 50), as by supplyingin line 64 synchronizing pulses derived from the repetition frequency ofthe radar, with a suitable delay as above explained. As thus arranged,the cell 50 will perform the dual functions of shutter action and ofcolor modulation, while the cell 51 intensitymodulates the light passedby the cell 50, but it will be understood that the color-modulatingaction may also be caused to take place in cell 51 (in which case cell51 performs the dual functions of intensity and color modulation), andthat, if desired, the frequency modulation and the intensity modulationmay be effected in the reversed order of cells (i.e. in cells 5:l-50,respectively). Further alternatively, it may in certain cases beadvantageous to impress the frequency-modulated signals (i.e. tocolormodulate) on both cells 50-51.

in the further alternative arrangement of Fig. 5, I employ a singleultrasonic cell 90, excited by a crystal 91 to which the output circuit28 of Fig. 3 may simultaneously supply both amplitude-modulated (A) andfrequency-modulated (F) signal components, based on the same carrierfrequency N. The system of Fig. 5 may otherwise resemble that of Fig. 1,except for omission of the shutter means 9; corresponding parts havetherefore been given the same reference numerals in the drawing. in Fig.5, shutter action is replaced by immobilizing action, achieved by meansof a rotating mirror polygon on a transverse axis perpendicular to thedirection of sound propagation in cell 90, and continuously driven at arate corresponding to the pulse-repetition or line frequency impressedat 91, divided by the number of mirror faces on prism 92; suchsynchronism with radar 38 is suggested at 94. The polygon 92 will beunderstood to produce elfective immobilization of any video signalstravelling in cell 90, so as to develop a continuously viewable displayof these signals in the image of cell 90, projected on screen or film93. As previously described, intensity and color modulation willcharacterize the display.

In Fig. 4A, there are illustrated modified electrical connections to theoptical configuration of Fig. 4, and for this reason, parts have beenidentified with corresponding reference numerals. In Fig. 4A, preferenceis indicated for feeding one cell (51) with both the amplitude andfrequency modulated signals, and for applying synchronizing pulses, asfrom line 39 of Fig. l, to the other cell (50). The resultant action inthe latter cell (50) is one of immobilization, as achieved by therotating polygon of Fig. 5.

75 of aheight-finding radar 76 may be caused to drive a potentiometer 77across which a D.C. voltage is applied for appropriately setting thecolor-modulation input to circuit 28. The video output may be fed to theamplitude-modulation input to circuit 28. Synchronizing data foroptical-shutter operation may be available from the radar at 79. Inoperation, it will beseen that color modulation of the display may begoverned solely by the instantaneous position of the computed-elevationoutput of the radar.

In a further application of my invention, color modulation of thedisplay may be caused to reflect instantaneous phase-shift phenomena; inradar applications, such use may provide a means of recognizing targetsurface or orientation characteristics from the color of a displayedtarget echo. To produce such indications I may employ the circuit ofFig. 10, which resembles the circuit of Fig. 8 except for-the inclusionof phase-discriminating means 80. The phase-discriminating means 80 mayfeed the frequency (color)-determining end of circuit 28 with signals ofvarying amplitude, reflecting the instantaneous phase condition ofreceived echoes, while the video output of the receiver is applied tothe amplitude-determining end of circuit 28.

It will be appreciated that I have described improved means for thesimultaneous display of a plurality of variables, in a manner providingeffectively an increased dimension in the interpretability of thedisplay. The incorporation of my invention involves little or no addedcomplexity over that required for certain black-and-white displays.Furthermore, the described ultrasonic colormodulation method has thebasic advantage (over other displays which rely solely on threeparticular colors) of offering an infinite and continuous gamut ofcolors, steadily varying from one spectral color to the next, throughoutthe whole spectrum; this fact inherently also permits adaptation of themethod to objective color-discriminating systems of far highercolor-resolving power than that of either the human eye or photographiccolor films.

While I have described my invention in detail for the preferred formsshown, it will be understood that modifications may be made within thescope of the claims which follow.

I claim:

1. In a radar, a receiver having a video output and a synchronizingoutput for a synchronized presentation of the video information, therebeing a fresh train of video signal for each transmission pulse andthere being a synchronizing signal for each such train, ultrasoniclight-cell display means including a color-separating diaphragm forarresting the projection of all except a relatively small part of thelight spectrum developed upon excitation of said ultrasoniccell means,shutter means for effectively immobilizing transients along said cellmeans, said shutter means being connected for operation by thesynchronizing output of said receiver, continuously variablefrequency-modulating means connected to said cell means, and meansconnecting the video output of said receiver to saidfrequency-modulating means.

2. A radar according to claim 1, in which amplitudemodulating means areprovided for said cell means, said amplitude-modulating means beingconnected for operation in response to the video output of saidreceiver.

3. In a radar-display device of the character indicated, a source oflight, ultrasonic-cell lightmodulating means including optics and adiaphragm forprojecting a colored image of said cell in accordance withthe instantaneous excitation of said cell, continuously variablefrequencymodulating and amplitude-modulating means for said cell, andmeans including a network for simultaneously supplying image-producingsignals to said frequencymodulating and to said amplitude-modulatingmeans.

4. A device according to claim 3, in which said network includes avoltage-divider output, and means for selectively independentlyconnecting said frequencymodulatingmean's andsaid amplitudeeinodulatingmeans to separatepoints onv said: voltage-divider output.

- 5 IA; device according to claim 3, in which said network is nonin ar,

6. In a radar, receiver means including decoding means responsive to apreselected pulse coding, ultrasonicscell light-modulating color-displaymeans including frequencymodulating means responsive to an operation ofsaid decoding means, whereby signals elfective to operate said decodingmeans may cause characteristic color modulations in said display.

7. In a radar, receiving means including a frequency discriminatorresponsive to carrier-frequency deviations in received pulses, displaymeans including ultrasonic-cell color-modulating means, andfrequency-modulating means for said cell means and connected foroperation in response to the output of said discriminator.

8'. A device according to claim 7, in which amplitudemodulating meansare provided for said cell means and are connected for response to thevideo output of said receiver.

9. In a height-finding radar, receiving means including a video outputand a computed-elevation output, means for modulating the video outputwith the computed-elevation output, frequency-modulating means driven bysaid modulated video output, and display means including ultrasonic-cellcolor-modulating means responsive to said frequency-modulating means.

10. In a radar, receiving means including a phase-discriminatorresponsive to phase displacements in the carrier frequency of receivedpulses, display means including ultrasonic-cell color-modulating means,and frequencymodulating means for said cell means and connected foroperation in response to the output of said discriminator.

11. A device according to claim 3, in which said network is linear.

12. In a radar display deviceof the character indi cated, delay-linemeans comprising ultrasonic-cell means, frequency-modulating andamplitude-modulating means for said delay-line means, means forinstantaneously sampling a substantial part of saidultraso'nic-cellmeans,

and optics responsive to the action of said sampling means 7 foroptically displaying the instantaneously sampled information in saiddelay-line means.

13. In a radar, a receiver having a video output and a synchronizingoutput for a synchronized presentation of the video information,ultrasonic-light-cell display means including a color-separatingdiaphragm for arresting the projection of all except a relatively smallpart of the light spectrum developed upon excitation of said ultrasoniccell means, mirror means for effectively immobilizing transients alongsaid cell means, means synchronized to the pulse-repetition frequency ofsaid radar for driving said mirror in a rotary sweep about an axissubstantially transverse to the propagation axis of the light reflectedby said mirror means, and frequency-modulating means for said cell meansand responsive to the video output of said receiver.

14. In a radar, a receiver having a video output and a synchronizingoutput for a synchronized presentation of the video information,ultrasonic-light-cell display means including a color-separatingdiaphragm for arresting the projection of all except a relatively smallpart of the light spectrum developed upon excitation of said ultrasoniccell means, a mirror polygonal prism mounted on a rotary axis generallytransverse to the propagation axis of light reflected thereby, means forcontinuously rotating said prism and including a synchronizingconnection with said radar, and continuously variable frequency- 16. Ina radar, display means including a source of light, ultrasonic-celllight-modulating means including optics and a diaphragm for projecting acoloredimage of said cell; a network responsive to received radardata-and including means for exciting said cellwith a carrier frequency,and means continuously variably responsive to said data forfrequency-modulating said carrier frequency,

References, Qiied in the file ofithis patent a UNITED STATES PATENTSAyres May 23, 1950 Rosenthal July 4, 1950 Hall et a1. May 20, 1952

